Diesel/electric marine propulsion systems are known, whose power supply has synchronous generators which are accommodated at some suitable point in the vessel's hull, and which themselves feed converter-fed synchronous or else asynchronous motors. The electric motors which drive the vessel propellers may, for example, be arranged as in-board motors, and may drive the vessel propellers via shaft systems.
Furthermore, pod propulsion systems are known, which have a synchronous motor with permanent-magnet excitation, arranged in a motor gondola which can be rotated. The motor gondola is arranged outside the vessel's hull and may have one or two vessel screws. The heat losses from the electric motor are in this case dissipated solely by the external surface of the motor gondola to the sea water. The asynchronous motors and generators have air/water heat exchangers.
Furthermore, JP 63217969 and JP 04304159 disclose marine propulsion systems for two vessel propellers including an associated so-called “homopolar motor”, which comprises two disc rotors or cylindrical rotors through which direct current flows in opposite directions via brushes, and in which a torque is produced in the field of a superconducting coil.